1. Field of the Invention
The present invention relates to a data communications system, an information processing terminal, an IC (Integrated Circuit) card, a reader/writer, and a program that are capable of wireless communication in a non-contact manner.
2. Description of the Related Art
Recently, information processing terminals, such as IC tags and IC cards capable of wireless communication in a non-contact manner and mobile phones having these IC cards, have been gaining popularity. These IC tags are used as embedded in price tags of commercial products for electronic reading the prices thereof, for example. IC cards are used to record electronic money information or the like for the application to the payment of purchased goods, for example. Attaching such an IC card function to information processing terminals in the form of an IC chip allows the inquiry for the balances of electronic money in each IC card through the information processing terminal, thereby expanding the application thereof.
In updating the information held in an information processing terminal attached with the IC card function described above, the user owning the information processing terminal first holds the IC card attached to the information processing terminal over a reader/writer that is continuously outputting a signal carrier. Then, the IC card, having detected the signal carrier being outputted from the reader/writer, establishes wireless communication with the reader/writer, thereby updating the data held in the information processing terminal as directed by a command issued from the reader/writer. The processing mainly based on such a reader/writer allows the user to complete update processing without executing a special operation.
In the data communication between the above-mentioned information processing terminal and reader/writer, the wireless control block of the IC card is typically in a command wait state; when the wireless control block receives data from the reader/writer, the wireless control block holds the received data and then enters the command wait state again. When the wireless control block receives a data transfer request from the controller of the information processing terminal, the wireless control block transmits the requested data held therein to the controller of the information processing terminal (refer to Japanese Patent No. 3617509 for example).
However, the above-mentioned communications processing supports only the unidirectional data transmission and reception request for the IC card and therefore disables the IC card to issue commands to the reader/writer.
The reader/writer is able to recognize the presence of each IC card only after receiving a response to a command (especially, a polling command) issued by the reader/writer. Therefore, in order to capture the IC card, the reader/writer has to continuously transmit a polling command at predetermined time intervals. If there are a plurality of IC cards within a communicable range of the reader/writer, namely, if a plurality of IC cards are held over the reader/writer in a stacked manner, for example, there may occur a collision between the responses from these IC cards to the polling command, thereby requiring some measures for the prevention of the collision.